To switch to an aftermarket xenon system you must discard the other, perfectly good xenon light AND buy two 740 headlamp assemblies (because the low beam lense on the xenon 750 won't accept a bulb).

Just want to know why someone would want to switch from Xenon to Halogen when Xenon is proven to be a better light (throws further, more accurate color rendering and longer lasting)?

Eric
88' 750il HID Converted

My post regarding rewiring expensive xenon lights for standard 12v has generated some interest, so now I'm posting instructions for how to do it.

Before proceding, you will need a complete headlight assembly for the same year 740. (low beam lamp, high beam lamp mounted in assembly). you'll also need a 12v light relay, such as for a set of aftermarket fog lights

I'm assuming a certain amount of electrical knowledge, such as knowing what a relay is for.

The headlight assembly on each side is fed by a 4-wire harness which connects to the chassis wiring via a round, twist-on connector near each assembly. Disconnect the twist on connector and also disconnect the feed to the high beam. Now remove the entire assembly.

The xenon electrics consist of a ballast unit mounted on a metal bracket in the middle of the assembly, and an igniter unit mounted on the low beam lense. Cut the 4-wire harness where it goes into the ballast unit. Remove the bracket holding the ballast assembly. Save the bracket and discard the remainder of the old headlight assembly

The wire color codes for the 4-wire harness are as follows:

Brown = 12v negative(ground)
Red = 12v primary (unswitched)
yellow/green = 9v (switched)--left (driver US) side only
yellow/blue = 9v (switched)--right (pass US) side only
yellow= 12v (switched)

Using the wiring diagram which came with the relay, splice the relay into the red and yellow wires. You can run a separate, secondary ground to the relay, or take a ground off of the brown wire. Mount the old ballast bracket on the 740 headlight assembly and mount the relay on the bracket.

Wire a standard, aftermarket plug for a 9005 high beam (yes, high beam) into the brown wire and the primary lead coming off the relay. You now should have a standard, switched 12v system which can be plugged into the low beam lense of the 740 assembly.

Use a PIAA or Solarus fax xenon 9005 bulb. Don't worry, it is safe even though the bulb technically is a "high beam" bulb. The lense is a special optical lense which cuts off glare to oncoming drivers and your car will be DOT compliant even running a high beam bulb in the low beam lense.

The remaining "loose end" is the 9v wire. Buy a couple of small, 12v bulbs at radio shack and wire them in parallel, with one side wired to the 9V lead and the other wired to ground. This will put a load on the 9v system even though the lamps will not light. It keeps the "low beam" warning from coming up on the instrument panel display.